“Murder Hornets”

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Lately there has been a lot of alarmist news reports about “murder hornets.” I thought I’d weigh in.

“Murder hornets” is the name given to the Asian giant hornet, Vespa mandarinia. Interestingly, there is no English common name for Vespa mandarinia. “Murder hornet” was coined by the media. In Japanese, this hornet is referred to as “great sparrow bee.” (Much nicer name than “murder hornet,” eh?) In Chinese, it is called “tiger head bee.” (But note: hornets are NOT bees! Check out the differences between bees and hornets here.)

The Asian giant hornet is one of the largest wasps in the world: queens can be 2 inches long with a wingspan of 3 inches. Workers are a bit smaller at 1.5 inches long. As their name implies, these wasps are found in Asia, specifically in parts of Japan, China, India, and Sri Lanka. But they have hit the news because they were recently found in British Columbia, Canada, and Washington state.

Close up of an Asian giant hornet. Photo source: National Geographic.
Asian giant hornets attacking a honeybee hive. Photo source: Scientific American.

Why are they called “murder hornets?” Asian giant hornets need to feed protein to the baby hornets in their nest so they can grow into adults. Where do they get the protein? From the bodies of other insects, particularly honeybees. Once an Asian giant hornet finds a honeybee hive, she’ll start chopping the heads off the honeybees using her huge mandibles (mouthparts). The hornet is after the honeybee’s thorax, which is the middle part of the body which is rich in protein because it contains all the honeybee’s flight muscles. The hornet turns the thorax into a “meatball” and carries it back to her nest.

When an Asian giant hornet finds a honeybee hive, she will wipe her rear end against the hive, leaving a pheromone, or chemical signal, which will alert her sister hornets to join in on the massacre. If enough sisters join in, they can slaughter the honeybee colony. A group of 20-30 Asian giant hornets can kill 5,000 to 25,000 honeybees in a few hours. (There are about 100 worker hornets and one queen hornet in an Asian giant hornet nest.) Once the hornets have slaughtered the honeybees, they will pilfer all of the larvae (baby honeybees) and bring them back to their nest to feed their own babies, since larvae are also high in protein.

However, the poor honeybees are not defenceless. Japanese honeybees (Apis cerana japonica) have lived with the Asian giant hornet for a long time and has a pretty cool strategy for fending off these murderers. Japanese honeybees can smell the pheromone that an Asian giant hornet leaves on their hive, and they start assembling the troops. They will gather in the hundreds, and when the hornet is entering the hive they will completely surround her, forming a “bee ball.” About 500 honeybees form a tight ball around the hornet, and they buzz their wing muscles to raise their body temperature so much that they cook the hornet to death! Scientists found that the temperature of a bee ball can rise to 47 degrees Celsius, which is lethal to the hornet but not to the bees. The hornet also suffocates with all of the carbon dioxide produced by the honeybees.

Left: A “bee ball” of about 400 honeybees surrounding an Asian giant hornet. Right: A dead Asian giant hornet and a few honeybees after their victory. Photo source: Nature journal.

Of course, if too many Asian giant hornets descend upon the honeybee hive at once, the honeybees can’t make enough bee balls to fend off the hornets, and they lose the battle.

So, why is the media freaking out about “murder hornets?”

Murder hornets will kill all the honeybees!

Yes, honeybees in North America would be in trouble if attacked by Asian giant hornets. Honeybees in North America are a different species from the ones in Japan who have developed the bee ball strategy. Here, our honeybees are Apis mellifera, the European honeybee, and they have not had to deal with Asian giant hornets. So, they don’t know the strategy of forming a ball to cook and suffocate the intruder to death. Our honeybees would be slaughtered by Asian giant hornets. BUT…there has been only a handful of sightings of Asian giant hornets in British Columbia and Washington. That’s it. Authorities are taking measures to get rid of the hornets if they are seen.

Murder hornets are dangerous to humans! They sting! They can kill us!

Yes, like all other hornets, Asian giant hornets can sting. And because they are so big, their sting can really pack a punch. There are reports that they can sting through the protective suits that beekeepers wear. BUT…like bees and other hornets, they will only sting if threatened (for example, if you swat at them), and if they feel that their nest is threatened. There is also a statistic floating around that “murder hornets” kill about 50 people a year. BUT…this includes all of Asia where the hornet is found, which is a huge swath of land. AND…to put things in perspective, an average of 62 Americans are killed each year by bees and wasps, due to allergic reactions (not all people are allergic to stings).

Murder wasps will multiply and take over the world!

Relax. As mentioned, they have only been found in a few places in British Columbia and Washington. If any good can come from the viral spread of the sensationalist news stories, it’s that people will be more aware and can help spot these hornets if they do start to multiply.

How did “murder hornets” end up in North America, anyway? We’re not sure. Some experts suspect that they hitchhiked on cargo that was shipped from Asia. Interestingly, that’s how some bumble bee species were thought to become established in some parts of the world!

References

Ono, M., Igarashi, T., Ohno, E. & Sasaki, M. (1995). Unusual thermal defence by a honeybee against mass attack by hornets. Nature, 377, 334-336.

Skvarla, M. J. (2020, May 6). Asian giant hornets. PennState Extension. Retrieved May 8, 2020 from https://extension.psu.edu/asian-giant-hornets